Method of and device for generating an image having a desired brightness

ABSTRACT

The present invention relates to a method of generating an image having a desired brightness, which image is generated by means of a device provided with at least one light source, at least one electro-optical light modulation panel and at least one light-control device. The light from the light source is converted into an image having a desired brightness via at least the electro-optical light modulation panel and the light-control device. The image to be projected is analyzed in a regulator, whereafter the electro-optical light modulation panel and the light-control device are driven, while a too bright image is generated by means of the electro-optical light modulation panel, which image is converted by means of the light-control device into an image having a desired brightness and a desired contrast.

This is a continuation of Ser. No. 09/389,177 filed on Sep. 2, 1999, nowU.S. Pat. No. 6,631,995.

The invention relates to a method of generating an image having adesired brightness, which image is generated by means of a devicecomprising at least one light source, at least one electro-optical lightmodulation panel and at least one light-control device, the light fromthe light source being converted into an image having a desiredbrightness via at least the electro-optical light modulation panel andthe light-control device.

The invention also relates to a device which is suitable for generatingan image having a desired brightness by means of such a method, whichdevice comprises at least one light source, at least one electro-opticallight modulation panel and at least one light-control device.

In such a method and device known from U.S. Pat. No. 5,597,223, thelight-control device comprises a diaphragm having an adjustableaperture. The device is applicable in a light or a dark ambience, withthe aperture size being adjusted in dependence upon a light or a darkambience, such that bright images or images which are rich in contrastare accentuated.

However, the aperture size is not optimized for each image. When, forexample, an LCD is used as an electro-optical light modulation panel,the contrast in an image is directly dependent on the desired brightnessof this image. When an image to be projected has a relatively lowbrightness, the LCD is driven accordingly. At a desired, relatively lowbrightness, the realized contrast is relatively low due to physicalproperties of the LCD. Consequently, the contrast that can be maximallyrealized with the LCD cannot be achieved at a desired, relatively lowbrightness.

It is an object of the invention to provide a method and a device withwhich a desired brightness and a desired contrast can be realized foreach image.

In the method according to the invention, this object is achieved inthat the image to be projected is analyzed in a regulator, whereafterthe electro-optical light modulation panel and the light-control deviceare driven, and a too bright image is generated by means of theelectro-optical light modulation panel, which image is converted bymeans of the light-control device into an image having a desiredbrightness and a desired contrast.

By analyzing preferably each image prior to driving the electro-opticallight modulation panel, the light modulation panel can be subsequentlydriven in such a way that a too bright image having a desired contrastis generated by means of this panel. Simultaneously, the light-controldevice, which comprises, for example, a diaphragm or a light modulationpanel, is driven in such a way that the image generated by means of thelight modulation panel and the light-control device has both the desiredcontrast and the desired brightness.

In the device according to the invention, the object is achieved in thatthe device comprises a regulator for analyzing the image to beprojected, driving the electro-optical light modulation panel forgenerating a too bright image, and driving the light-control device forconverting the too bright image into an image having a desiredbrightness and a desired contrast.

By driving the light modulation panel as maximally as possible, amaximal brightness and thus a maximal contrast is obtained. Thebrightness is reduced to the desired level by means of the light-controldevice.

For an image having large dark areas and large highlights areas, thedark areas can be made perceptually darker by generating a too darkimage by the panel, and converting the image into one having the desiredbrightness and contrast by using the light control device to increaselight from the light source.

An embodiment of the device according to the invention is characterizedin that the device comprises at least two electro-optical lightmodulation panels and one light-control device, by means of which imagesgenerated on the light modulation panels are simultaneously convertible.

Each light modulation panel is applicable for a different color of theimages to be projected. Since each light modulation panel is associatedwith a light-control device, the light modulation panel can be optimallydriven separately for each color by means of the regulator.

These and other aspects of the invention are apparent from and will beelucidated with reference to the embodiments described hereinafter.

In the drawings,

FIG. 1 shows a first embodiment of a device according to the invention,

FIG. 2 shows a second embodiment of a device according to the invention,

FIG. 3 shows a third embodiment of a device according to the invention,and

FIG. 4 shows a fourth embodiment of a device according to the inventioncomprising one color single light modulation panel of the reflectivetype.

Corresponding components in the Figures are denoted by the samereference numerals.

FIG. 1 shows a device 1 according to the invention, comprising a lightsource 2, three electro-optical light modulation panels 3, 4, 5 withwhich a green G, a red R and a blue B part, respectively, of an image tobe projected is realized, and a light-control device 6 arranged betweenthe light source 2 and the light modulation panels 3-5. A folding mirror7 and a PBS 8 (Polarizing Beam Splitter) are arranged between the lightsource 2 and the light-control device 6. The light-control device 6 maybe a diaphragm, but in the embodiment shown here, the light-controldevice is provided with a twisted nematic cell having a polarizer at anexit side. Lenses 9, (dichroic) folding mirrors 10 and polarizationfilters 11 are arranged between the light-control device 6 and the lightmodulation panels 3-5. The lenses 9, (dichroic) folding mirrors 10 andfilters 11 are known per se and will therefore not be described ingreater detail. The device 1 further comprises a projection lens 12.Filters 11 and (dichroic) folding mirrors 10 are also arranged betweenthe light modulation panels 3-5 and the projection lens 12.

The device 1 further comprises a regulator 13. The regulator 13 has avideo signal input 14 which is connected to a video signal analyzer 15and to a video signal amplifier 16. The video signal analyzer 15 is alsoconnected to the video signal amplifier 16. The video signal amplifier16 has a video signal line 17 which is also connected to the lightmodulation panels 3-5. The regulator 13 further comprises a drive module18 which is arranged between the video signal analyzer 15 and thelight-control device 6.

The operation of the device 1 will now be briefly elucidated. The videosignal input 14 supplies the information about the images to beprojected to the regulator 13. This information is analyzed in the videosignal analyzer 15, determining the desired brightness and the desiredcontrast of the complete image or of parts of the image. Subsequently,the video signal analyzer 15 drives the video signal amplifier 16 andthe drive module 18 which in their turn drive the light modulationpanels 3-5 and the light-control device 6, respectively.

The video signal amplifier 16 drives the light modulation panels 3-5 insuch a way that, in the absence of the light-control device 6, an imagewould be obtained which would have a too high brightness. However, thecontrast of such an image would have a desired value. The drive module18 drives the light-control device 6 completely or for each part of theimage to be projected, such that the brightness of the projected imagecorresponds to the desired brightness. The regulator 13 is preferablybased on statistic information relating to the amplitude range of thevideo signal.

FIG. 2 shows a device 20 according to the invention, comprising a lightsource 2, light modulation panels 3-5 and a projection lens 12. Thedevice 20 further comprises lenses 9, (dichroic) folding mirrors 10, aPCS 21 and an integrator 22, arranged between the light source 2 and thelight modulation panels 3-5. The device 20 further comprises a dichroicprism 23 arranged between the light modulation panels 3-5 and theprojection lens 12. Moreover, the device 20 comprises threelight-control devices 24 arranged on a side of the light modulationpanels 3-5 remote from the prism 23. The light-control devices 24 andthe light modulation panels 3-5 can be driven by means of a regulator,such that, per color green G, red R and blue B, the associated lightmodulation panel 3-5 is driven in such a way that a too bright imagehaving a desired contrast is obtained, which image is converted by meansof the associated light-control devices 24 into an image having adesired brightness.

FIG. 3 shows a third embodiment of a device 30 according to theinvention, comprising a light source 2, reflective light modulationpanels 3-5 and a projection lens 12. The device further comprises lenses9, (dichroic) folding mirrors 10, a PCS 21, an integrator 22 andpolarizing beam splitters 31, arranged between the light source 2 andthe light modulation panels 3-5. The polarizing beam splitters 31 andthe dichroic prism 23 are arranged between the light modulation panels3-5 and the projection lens 12. The device 30 further comprises aliquid-crystal shutter 32 which can be controlled separately for each ofthe three colors and is arranged on a side of the projection lens 12remote from the light modulation panels 3-5. Also in the device 30 shownin this embodiment, the light modulation panels 3-5 are driven at abrightness which is relatively too high, whereafter the desiredbrightness of the image to be projected is generated per color by meansof the shutter 32 operating as a light-control device.

Although not mentioned in the description of FIGS. 1 and 2, bothembodiments may be provided with an integrator arranged between thelight source 2 and the PBS 8.

It is alternatively possible to use the method and the device in systemswhich are not provided with a projection lens 12.

Dependent on the desired quality of the images to be projected, thelight-control device can influence the brightness of the image in itstotality, or it can influence the brightness of parts of the image to beprojected. As smaller parts of the image can be influenced by thelight-control device, a higher quality of the image to be projected canbe realized.

It is alternatively possible to provide a light source drive unit as alight-control device, by means of which the brightness of the lightsource can be controlled per image. Light sources which do not require aconstant power level are, for example, Xenon arc lamps and LEDs.

All embodiments described up to now show a device comprising three lightvalves 3-5. However, it is possible to have a device comprising only onelight modulation panel, monochrome or color. A color single lightmodulation panel can for example by illuminated color sequentially bymeans of a color wheel, by scrolling bars or by means of threedifferently colored lamps. In case of a color wheel or three differentlight sources, the image can be influenced for each color independently.Namely, the segments in the color wheel or the time that each of thelamps is lit can be varied for each color. In case of scrolling bars, itis more difficult to influence the intensity of the colors in the imageindependently as the panel is illuminated by two bars simultaneously.

When the device comprises three light modulation panels and one lightsource, independent control of the intensity of the colors in the imageis not possible. When the intensity of the light source is changed, thethree colors will be influenced simultaneously.

Another embodiment in which independent control for each color ispossible is shown in FIG. 4.

FIG. 4 shows an embodiment of a device 40 according to the inventioncomprising one single light modulation panel 42 of the reflective type.Said panel can be for example a reflective LCD-panel or a DMD-panel.Image information to be projected is provided from a video source 44 viaprojector electronics 46 to the panel 42, on the one hand, and to alight source controlling device 48, on the other hand, forsynchronization. The light source comprises three different lamps 50, 52and 54, one for each primary color. The light source controlling device48 is connected to a programmable power supply 56, 58, 60 for the lamps50, 52 and 54. Via lenses 62 and a prism illuminator 64, the light fromthe light source is incident on the light valve 42. The prismillumination 42 may be a PBS in case the light valve is an LCD panel andmay be a prism based on TIR in case the light valve is a DMD. Aftermodulation by the light valve 42, the light to be projected reaches theprojection lens 68. By flashing each of the lamps in a time interval of,for example 16 ms, as is indicated in the inset, and by varying the timeinterval for the individual lamps, the colors can be variedindependently in the image to be projected. The video data to beprojected for each color are field sequentially provided to the lightmodulation panel.

1. A method of generating a desired image, comprising: analyzing a firstimage to determine a desired brightness and a desired contrast for saidfirst image; providing an illumination beam from a constant intensitylight source; modulating said illumination beam to produce an image beamhaving said desired contrast; and optically adjusting a one of saidillumination beam and said image beam to form said desired image havingsaid desired brightness.
 2. The method as claimed in claim 1, whereinthe analyzing is performed by a regulator.
 3. The method as claimed inclaim 1, wherein the step of modulating is performed by a lightmodulator panel.
 4. The method as claimed in claim 1, wherein the stepof optically adjusting is performed by a light control device.
 5. Themethod as claimed in claim 1, wherein a brightness and a contrast ofsaid desired image are adjusted substantially independently of eachother.
 6. The method as claimed in claim 1, wherein a contrast of saiddesired image is independent from a background illumination level. 7.The method of claim 1, wherein the first image does not cover a completerange of gray levels producible by an image processing apparatusperforming said step of modulating; the image beam covers a larger rangeof gray levels than the first image, while being within said completerange; and whereby, the desired image has the larger range of graylevels with the desired brightness.
 8. The method of claim 7, whereinthe image processing apparatus comprises at least one light modulationpanel and wherein the image beam comprises image modulation informationwithin the at least one modulation panel.
 9. The method of claim 7,wherein the step of modulating results in a brightness level that causesthe image beam to lie within parameters achieving a maximum dynamicrange of at least a portion of the image processing apparatus.
 10. Themethod of claim 9, wherein the step of optically adjusting relates to asecond portion of the image proceasing apparatus.
 11. A method forproducing an output image in a device comprising a constant intensitylight source and at least one light modulator, the output imageresulting from passing light from the constant intensity light sourcethrough the light modulator, the method comprising: analyzing an inputimage to derive a desired contrast and desired brightness; adjusting thelight modulator to a setting which would normally not result in thedesired brightness, but would result in the desired contrast; opticallyadjusting the brightness of the output image to retain the desiredcontrast achieved by the light modulator while attaining the desiredbrightness.
 12. An image producing device for generating an outputimage, the image producing device comprising: a video input; at leastone constant intensity light source, having a given normal brightnessvalue; at least one light modulator, responsive to the video input foradding image data from the video input to light from the light source;means for a video signal analyzer performing video signal processingincluding: analyzing the video input to derive a desired contrast and adesired brightness; supplying at least one first control signal to causethe light modulator to be adjusted to achieve the desired contrast, buta brightness other than the desired brightness with the constantintensity light source at the given normal brightness value; andsupplying at least one second control signal to cause an optical abrightness adjustment optically or by varying a time interval offlashing of the at least one constant intensity light source in order toachieve the desired brightness in the output image in view of theadjustment of the light modulator; so such that the output image hasboth the desired contrast and the desired brightness.
 13. The imageproducing device of claim 12, further comprising: a light sourcecontrolling device, the video signal analyzer supplying the at least onesecond control signal to cause the light source controlling device tovary a time interval of flashing of the at least one constant intensitylight source.
 14. The image producing device of claim 12, wherein theoutput image is an output color image, and the at least one constantintensity light source comprises: a red constant intensity light source,having a normal red brightness value; a green constant intensity lightsource having a normal green brightness value; and a blue constantintensity light source having a normal blue brightness value, whereinthe adjusting includes independently varying time intervals of flashingof the red, green, and blue constant intensity light sources to formsaid output color image such that that the output color image has boththe desired contrast and the desired brightness for each of red, green,and blue components.
 15. The image producing device of claim 12, whereinsaid desired contrast is maximal contrast.
 16. The image producingdevice of claim 12, wherein the video signal analyzer supplies the atleast one second control signal to one of a diaphragm and the lightmodulator to cause said brightness adjustment such that that the outputimage has both the desired contrast and the desired brightness.
 17. Theimage producing device of claim 12, wherein the analyzing of the videoinput derives a desired contrast and a desired brightness for a part ofthe output image.
 18. The image producing device of claim 12, furthercomprising: A light control device receiving the at least one secondcontrol signal and adjusting brightness of a part of the output image.